/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {

public:
    ListNode* deleteDuplicates(ListNode* head) {

        ListNode pre(0);
        ListNode* cur=&pre;
        while(head){
            int cnt=1;
            int val=head->val;
            head=head->next;
            while(head && head->val==val){
                cnt++;
                head=head->next;
            }
            if(cnt<=1){
                cur->next=new ListNode(val);
                cur=cur->next;
            }

        }

        return pre.next;
    }
};
